As illustrated in FIG. 17, the steering apparatus for a vehicle is constructed so as to transmit rotation of a steering wheel 1 to an input shaft 3 of a steering gear unit 2, to push or pull a pair of left and right tie rods 4 as the input shaft 3 rotates, and thus to apply a steering angle to the front wheels. The steering wheel 1 is supported by and fastened to the rear end section of a steering shaft 5, and the steering shaft 5 is inserted in the axial direction through a cylindrical shaped steering column 6 and is supported by the steering column 6 so as to be able to rotate freely. The front end section of the steering shaft 5 is connected to the rear end section of an intermediate shaft 8 by way of a universal joint 7, and the front end section of the intermediate shaft 8 is connected to the input shaft 3 by way of another universal joint 9. In the example illustrated in the figures, an electric assist apparatus that reduces the operating force for operating the steering wheel 1 is assembled. Specifically, an electric motor 10 that functions as a power source for applying auxiliary power is supported by a housing 11 that is fastened to the front end section of the steering column 6. The output torque of the electric motor 10 is applied to the steering shaft 5 by way of a gear unit or the like that is provided inside the housing 11. Here, the forward-backward direction, left-right direction (width direction) and the up-down direction correspond to each of the directions of the vehicle unless otherwise noted.
The steering apparatus that is illustrated in FIG. 17 is a tilt and telescopic steering apparatus that comprises both a tilting mechanism for adjusting the up-down position of the steering wheel 1, and a telescopic mechanism for adjusting the forward-backward position of the steering wheel 1 in accordance to the size and operating posture of the driver. More specifically, the steering column 6 is supported by the vehicle body 12 so as to be able to pivotally displace around a pivot shaft 13 that is installed in the left-right direction. The steering column 6 is constructed by fitting together the rear section of an inner column 14 and the front section of an outer column 15, or in other words, by fitting the tip end sections of the inner column 14 and outer column 15 so as to displace relative to each other in the axial direction. The steering shaft 5 is constructed by fitting together with a spline joint the rear section of an inner shaft 16 that is supported on the inner diameter side of the inner column 14 so as to only be able to rotate, and the front section of an outer shaft 17 that is supported in the inner diameter side of the outer column 15 so as to only be able to rotate, such that torque can be transmitted and so that relative displacement in the axial direction is possible. A displacement bracket 18 that is fastened to the outer column 15 is supported by a support bracket 19 that is supported by the vehicle body 12 so as to be able to displace in the up-down direction and forward-backward direction.
A long hole 20 for telescopic adjustment that extends in the axial direction of the outer column 15 is formed in the displacement bracket 18. A support bracket 19 comprises a pair of support plates 21 that hold the displacement bracket 18 from both the left and right sides. Long holes 22 for tilt adjustment that extend in the up-down direction are formed in portions of these support plates 21 that are aligned with each other. An adjustment rod 23 is inserted through the long holes 22 for tilting adjustment and the long hole 20 for telescopic adjustment. The adjustment rod 23 comprises a pair of pressure sections that hold the pair of support plates 21 from both the left-right sides, and an expansion and contraction apparatus that operates according to the operation of an adjustment lever (not illustrated in the figure) is able to expand or contract the space between these pressure sections.
When adjusting the up-down position or forward-backward position of the steering wheel 1, the adjustment lever is rotated in a specified direction around the adjustment rod 23, which expands the space between the pair of pressure sections provided on the adjustment rod 23. As a result, friction force that acts between the inside surfaces of the support plates 21 and both side surfaces of the displacement bracket 18 decreases. In this state, it is possible to adjust the position of the steering wheel 1 within the range that the adjustment rod 23 is able to displace inside the long holes 22 for tilt adjustment, and the long hole 20 for telescopic adjustment. After adjustment, the adjustment lever is rotated in the opposite direction, which contracts the space between the pair of pressure sections provided on the adjustment rod 23. As a result, friction force that acts between the inside surfaces of the support plates 21 and both side surfaces of the displacement bracket 18 increases, and the steering wheel 1 is maintained in the adjusted position.
In the steering apparatus illustrated in FIG. 17, in the state when the apparatus is assembled in the vehicle body 12 (normal state), the range in which relative displacement in the axial direction between the inner column 14 and outer column 15 is possible is regulated by the telescopic adjustment range (range in which the adjustment rod 23 is able to displace inside the long hole 20 for telescopic adjustment).
On the other hand, in the state before assembly in the vehicle body 12, or in the state in which the support bracket 19 has become separated from the vehicle body 12 due to a secondary collision, the support bracket 19 is able to displace together with the outer column 15, so the range in which relative displacement in the axial direction between the inner column 14 and outer column 15 is possible is no longer restricted by the telescopic adjustment range. Therefore, there is a possibility that the inner column 14 and outer column 15 will undergo excessive relative displacement in the extending direction of the steering column 6.
In addition to the construction illustrated in FIG. 17, construction of a telescopic steering apparatus has also been conventionally known in which the front section of the outer column that fits around the outside of the rear section of the inner column is a partial cylindrical shape, and by rotating the adjustment lever in a specified direction, the diameter of the front section of the outer column is reduced, increasing the surface pressure between the inner circumferential surface of the front section of the outer column and the outer circumferential surface of the rear section of the inner column. In this construction, even in the state before assembly in the vehicle body, or in the state in which the support bracket has become separated from the vehicle body due to a secondary collision, relative displacement in the axial direction between the inner column and the outer column is prevented by the surface pressure between the inner circumferential surface of the front section of the outer column and the outer circumferential surface of the rear section of the inner column. However, when the adjustment lever is rotated in the opposite direction, and the surface pressure between the inner circumferential surface of the front section of the outer column and the outer circumferential surface of the rear section of the inner column is reduced, relative displacement between the inner column and the outer column becomes possible, and there is a possibility that there will be excessive relative displacement in the extending direction of the steering column.
Particularly, in the state before assembly in the vehicle body, when the inner column and outer column undergo excessive relative displacement in the axial direction and the tip end sections thereof become separated from each other, extra time is then required to reassemble the inner column and outer column. In JP 2012-001189 (A), construction of a steering column is disclosed in which the inner column and outer column are prevented from separation by connecting the inner column and outer column using a connecting wire. By employing this kind of construction, the inner column and outer column are prevented from undergoing excessive relative displacement in the axial direction. However, in this kind of construction, a connecting wire becomes necessary, so there is an increase in cost due to the increase in the number of parts.